1. Field of the Invention
This invention is related to a diaphragm pump and an anode stream recirculation system using such pump for a fuel cell, in particular, an anode stream recirculation system used in a proton exchange membrane fuel cell as well as the diaphragm pump used in such system, and most particularly, a hydrogen recirculation system and the diaphragm pump utilized in a proton exchange membrane fuel cell. The present invention eliminates certain elements required in the conventional anode stream recirculation system for a fuel cell and, thus reduces the cost for manufacture of the components of the fuel cell. Furthermore, this invention lowers the electrical energy required to operate the anode stream recirculation system so that the overall efficiency of electrical power generation for the fuel cell system can be promoted.
2. Description of the Related Art
With the rapid growth of civilization, the consumption of traditional energy resources, such as coal, oil and natural gas, increases rapidly. This results in serious environmental pollution and causes a series of environmental problems such as global warming and acid rain. It is now recognized that the existing natural energy resources are limited. Therefore, if the present rate of energy consumption continues, all existing natural energy resources will be exhausted in the near future. Accordingly, many developed countries are conducting research and development of new and alternative energy resources. The fuel cell is one of the most important and reasonably priced energy resources. Compared with traditional internal combustion engines, the fuel cell has many advantages such as high energy conversion efficiency, clean exhaust, low noise, and no consumption of traditional gasoline.
In brief, a fuel cell is an electrical power generation device powered by the electrochemical reaction of hydrogen and oxygen. Basically, the reaction is a reverse reaction of the electrolysis of water, to convert the chemical energy into electrical energy. The basic structure of a fuel cell, for example, a proton exchange membrane fuel cell, comprises a plurality of cell units. The structure of the cell unit generally illustrated in FIG. 1 comprises a proton exchange membrane (PEM) 10 at the middle, with the two sides thereof provided with a layer of catalyst 12, each of the two outsides of the catalyst 12 is further provided with a gas diffusion layer (GDL) 14. An anode plate 16 and a cathode plate 18 are further provided at the outermost sides adjacent to the GDL 14. After tightly combining all the above elements together, a cell unit is formed. For practical application of the fuel cell, a plurality of the above cell units are stacked and serially connected to provide sufficient power, as illustrated in FIG. 2. Therefore, two adjacent cell units can share a common polar plate 20, as illustrated in FIG. 3, which serves as the anode and the cathode for the two adjacent cell units, respectively. Accordingly, such a polar plate 20 is usually referred as a bipolar plate. Generally, as illustrated in FIG. 3, the two sides of the bipolar plate 20 are provided with many groove type gas channels 22 for transporting the gases for reaction, such as hydrogen and air (to provide oxygen), as well as transporting the reactants, such as water droplets or vapor, out of the bipolar plate 20.
One conventional gas supply system for use in a fuel cell comprises: a cathode gas supply system (such as an oxygen supply), and an anode circulation system (such as a hydrogen circulation system), as illustrated in FIG. 4. Atmospheric air may serve as a supply of the oxygen supply system 30, where air is filtered by a filter 32 and than pumped into the fuel cell 50 through a blower 34. Excessive air, upon reaction within the fuel cell 50, is discharged through a water recuperator 36. The water recuperator 36 may recuperate the minute amount of water contained within the discharged air, where the water is then directed to a cooling system 38. The useless heat generated by the fuel cell 50 is also transmitted to the cooling system 38. The coolant used in the cooling system 38 then re-enters the fuel cell 50 to provide sufficient cooling thereto.
The conventional anode circulation system includes: a hydrogen source 40 which regulates hydrogen input through a pressure regulator 42; a hydrogen pump 44 being provided at the other end of the fuel cell 50 for discharging excessive hydrogen, upon reaction within the fuel cell, and for pumping the hydrogen source 40 into the fuel cell 50. The excessive hydrogen is discharged through a humidifier 46, such as a bubbler, for increasing the humidity of the excessive hydrogen, then flows back into the piping of the hydrogen supply to be mixed with fresh hydrogen, and then repeats the same circulation. The water within the cooling system 38 can be transmitted to the water within the humidifier 46.
The hydrogen within the bipolar plate of the fuel cell must have adequate humidity such that the hydrogen ions (H+) after reaction can be carried through the PEM by the water vapor. The hydrogen ions then react with the oxygen at the other side of the PEM and the electrons provided from the outer circuit, to establish proton conduction. Generally, if the humidity of the hydrogen is too low, the PEM will be dehydrated, thus, the electrical resistance of the fuel cell will increase and the voltage of the fuel cell will decrease, which will result in the working life of the fuel cell being significantly shortened. If, on the other hand, the humidity of the hydrogen is too high, the channels for transporting the gases within the bipolar plate may be clogged by water droplets, which will stop the reaction of gases within the fuel cell and the performance of the fuel cell will be seriously impaired. Accordingly, in the anode stream recirculation system, a humidifier to adjust the humidity of the hydrogen is generally required.